Rational Design of Asymmetric Polymethines to Attain NIR(II) Bioimaging at >1100 nm

Hsiu Min Pan, Chi Chi Wu, Chun Yi Lin, Chao Shian Hsu, Yi Chen Tsai, Partha Chowdhury, Chih Hsing Wang, Kai Hsin Chang, Chieh Hsuan Yang, Ming Ho Liu, Yan Chang Chen, Shih Po Su, Yi Jang Lee, Huihua Kenny Chiang, Yang Hsiang Chan*, Pi Tai Chou*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


Organic molecules having emission in the NIR(II) region are emergent and receiving enormous attention. Unfortunately, attaining accountable organic emission intensity around the NIR(II) region is hampered by the dominant internal conversion operated by the energy gap law, where the emission energy gap and the associated internal reorganization energy λint play key roles. Up to the current stage, the majority of the reported organic NIR(II) emitters belong to those polymethines terminated by two symmetric chromophores. Such a design has proved to have a small λint that greatly suppresses the internal conversion. However, the imposition of symmetric chromophores is stringent, limiting further development of organic NIR(II) dyes in diversity and versatility. Here, we propose a new concept where as far as the emissive state of the any asymmetric polymethines contains more or less equally transition density between two terminated chromophores, λint can be as small as that of the symmetric polymethines. To prove the concept, we synthesize a series of new polymethines terminated by xanthen-9-yl-benzoic acid and 2,4-diphenylthiopyrylium derivatives, yielding AJBF1112 and AEBF1119 that reveal emission peak wavelength at 1112 and 1119 nm, respectively. The quantum yield is higher than all synthesized symmetric polymethines of 2,4-diphenylthiopyrylium derivatives (SC1162, 1182, 1185, and 1230) in this study. λint were calculated to be as small as 6.2 and 7.3 kcal/mol for AJBF1112 and AEBF1119, respectively, proving the concept. AEBF1119 was further prepared as a polymer dot to demonstrate its in vitro specific cellular imaging and in vivo tumor/bone targeting in the NIR(II) region.

Original languageEnglish
Pages (from-to)516-526
Number of pages11
JournalJournal of the American Chemical Society
Issue number1
StatePublished - 11 Jan 2023


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